(1) Field of the Invention
The present invention relates to a process for the preparation of neodymium or a neodymium alloy. More particularly, the present invention provides a process for preparing, at a low cost, high-purity neodymium or a high-purity neodymium/iron alloy, suitable as the starting material for an Nd-Fe-B type magnet which has recently attracted attention as a high-performance magnet.
(2) Description of the Related Art
A permanent magnet of the Nd-Fe-B system or Nd-Fe-Co-B system has recently been proposed as a relatively cheap high-performance permanent magnet (see Japanese Unexamined Patent Publication No. 59-46008 and Japanese Unexamined Patent Publication No. 59-64739). It is known that Nd used for the production of a permanent magnet of this type can be prepared by the calcium thermal reduction process or the fused salt electrolysis process (see, for example, Japanese Unexamined Patent Publication No. 62-63642). According to the calcium thermal reduction process, high-purity Nd can be obtained, but the process is defective in that the manufacturing cost is high. The present invention is directed to the production of Nd according to the fused salt electrolysis process.
The fused salt electrolysis process is roughly divided into a process using a chloride electrolysis bath and a process using a fluoride electrolysis bath. As the fused salt electrolysis process using a fluoride electrolysis bath, there is known the consumable electrode process for the production of an Nd/Fe alloy, in which iron is used as the cathode, carbon is used as the anode, the electrodes are formed to have a rod-like shape or a concentric shape, Nd.sub.2 O.sub.3 is electrolytically reduced in an appropriate fused salt electrolysis bath, and a metallic neodymium is deposited on the cathode of iron to alloy neodymium with iron (E. Morris et al, U.S. Bur. Min., Rep. Invest., No. 7146, 1968). Moreover, it is taught that there is a possibility that a fluoride of neodymium will be used as the starting neodymium compound (Morris et al, U.S. Bur. Min., Rep. Invest., No. 6957, 1967).
Furthermore, the fused salt electrolysis processes for the production of Nd are taught in Japanese Unexamined Patent Publication No. 61-159593, Japanese Unexamined Patent Publication No. 61-87888, and Japanese Unexamined Patent Publication No. 61-127884.
Generally speaking, however, the fused salt electrolysis process for the production of Nd is still at the first step of research and development, research has been made mainly on the laboratorial level, and the electrolysis process for the production of Nd has not been investigated on the commercial level. The present inventors are not aware of any reports concerning such investigations.
Under this background, the present inventors carried out research into the commercial-scale production of Nd by the fused salt electrolysis process, with a view to preparing same on an industrial scale and supplying Nd expected to be much in demand in the future as the starting material of a permanent magnet of the Nd-Fe-B system or Nd-Fe-Co-B system, and as a result, have now completed the present invention.